These are simple strategies to defeat Nightwatcher Merayl for the Family Familiar achievement. You can only fight these trainers when their World Quest is available. These strategies assume all of your pets are level 25 and of Rare quality.
Clobber. Spam Tidal Wave until Tideskipper dies. Switch to Penguin. Slippery Ice. Spam Ice Lance until Spirit dies. Use Slippery Ice again on the Undead round. Ice Lance until the Book dies. Clean up with Spawn if you have to.
Simply spam Arcane Blast and use Evanescence/Soul Ward when Curse of Doom has one round remaining. I was able to solo the whole fight with the Manafiend. If you think he’s about to die, you can hit Surge of Power and move on to another pet to finish the job.
Open with Thunderbolt and use it on cooldown. Spam Breath, and hit Decoy when Curse of Doom has one round remaining. It is possible to solo the whole fight with just the Dragonling. If it dies, bring in one of the other pets to clean up.
Plagued Blood. Tail Sweep until Breezy Book dies. Use Plagued Blood when Helpful Spirit comes out. Death and Decay. Immediately bring in Maggot. You want to get Spirit down fast so he doesn’t whittle down Shadeling in the background with Arcane Explosion. Spam Chomp until the Maggot dies. Bring out Shadeling and finish off Moth with a few Arcane Blasts.